[英]Rails: Eager loading for models three associations away
我想在表列中显示所有时间表以及相关类,合作伙伴和位置的表。
# view
<% @schedules.each do |schedule| %>
<%= schedule.date.strftime("%d %b %Y") %>
<%= schedule.klass.name %>
<%= schedule.partner.company %>
<%= schedule.partner.city.name %>
<%= schedule.start_time.strftime("%l:%M%P") %> -
<%= schedule.end_time.strftime("%l:%M%P") %>
<% end %>
# models
Schedule
belongs_to :klass
belongs_to :partner
Klass
belongs_to :partner
Partner
belongs_to :city
has_many :klasses
has_many :schedules
City
none
# controller Schedules
@schedules = Schedule.includes(:klass, :partner).order(:date, :start_time, :end_time)
不幸的是,页面加载后会多次运行city
查询。
SELECT "schedules".* FROM "schedules" ORDER BY "schedules"."date" ASC, "schedules"."start_time" ASC, "schedules"."end_time" ASC
SELECT "klasses".* FROM "klasses" WHERE "klasses"."id" IN (6, 1, 7, 9, 10, 3)
SELECT "partners".* FROM "partners" WHERE "partners"."id" IN (3, 4, 2)
SELECT "cities".* FROM "cities" WHERE "cities"."id" = $1 LIMIT 1 [["id", 23]]
SELECT "cities".* FROM "cities" WHERE "cities"."id" = $1 LIMIT 1 [["id", 24]]
我尝试了这个:
Schedule.includes(:klass, :partner).includes(:city)
但这给了我这个错误:
Association named 'city' was not found on Schedule; perhaps you misspelled it?
我已经阅读了有关Active Record查询的Rails指南,但对如何改进查询一无所知。 任何帮助表示赞赏。 谢谢。
Schedule
belongs_to :klass
belongs_to :partner
Klass
has_many :schedules
has_many :partners, through: :schedules
Partner
belongs_to :city
has_many :schedules
has_many :klasses, through: :schedules
City
has_many :partners
查询应该是
@schedules = Schedule.includes(:partner => :city).order(:date, :start_time, :end_time).select('partners.*, cities.name')
得到它了:
@schedules = Schedule.includes(:klass, partner: :city).order(:date, :start_time, :end_time)
结果:
SELECT "schedules".* FROM "schedules" ORDER BY "schedules"."date" ASC, "schedules"."start_time" ASC, "schedules"."end_time" ASC
SELECT "klasses".* FROM "klasses" WHERE "klasses"."id" IN (6, 1, 7, 9, 10, 3)
SELECT "partners".* FROM "partners" WHERE "partners"."id" IN (3, 4, 2)
SELECT "cities".* FROM "cities" WHERE "cities"."id" IN (23, 24)
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